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In economics and consumer theory, quasilinear utility functions are linear in one argument, generally the numeraire. Quasilinear preferences can be represented by the utility function u = x 1 + θ {\displaystyle u=x_{1}+\theta } where θ {\displaystyle \theta } is strictly concave. A useful property of the quasilinear utility function is that the Marshallian/Walrasian demand for x 2 , … , x n {\displaystyle x_{2},\ldots ,x_{n}} does not depend on wealth and is thus not subject to a wealth effect; The absence of a wealth effect simplifies analysis and makes quasilinear utility functions a common choice for modelling. Furthermore, when utility is quasilinear, compensating variation , equivalent variation , and consumer surplus are algebraically equivalent. In mechanism design, quasilinear utility ensures that agents can compensate each other with side payments.